Executive brief
Ech0 is an open-source authentication and identity management service. A vulnerability in its OAuth login flow allows attackers to redirect users to arbitrary paths on allowed hosts and capture their authentication credentials. An attacker can trick users into logging in via a crafted link, intercept the temporary authorization code, and trade it for the victim's access and refresh tokens—effectively hijacking their account.
Technical details
The vulnerability lies in parseAndValidateClientRedirect (internal/service/auth/auth.go:448), which validates OAuth redirect URIs by comparing only the scheme and host components against an admin-configured allowlist, ignoring path, query, and fragment. The caller-supplied redirect_uri is embedded into a signed state JWT at login time without validation. An attacker crafts a redirect_uri with a host matching an allowed origin but a path under attacker control; after OAuth provider exchange, Ech0 redirects the victim to that path with the one-time exchange code in the query string. If the code is leaked via Referer header, analytics, or an open redirect on the matched host, the attacker can exchange it at the public POST /api/auth/exchange endpoint for the victim's tokens. The vulnerability violates RFC 6749 §3.1.2 (exact redirect URI matching). Fixed in version 4.7.3.
Affected products
- lin-snow Ech0 through 4.5.6
Timeline
- 2026-05-03: disclosed
- 2026-04-01: patched: Fix released in version 4.7.3
- 2026-08-25: advisory